A seizure happens when the nerves in a person's brain act strangely. Nerves send information, partly through electrical signals. Usually, nerves in the brain (called neurons) do not fire at the same time. During a seizure, groups of nerves start firing together, too fast.[1] This causes there to be too much disorganized electrical activity in the brain.

Most people think a person with a seizure will shake and twitch. Some will, but there are also other kinds of seizures.[2]

Complex partial: The person "zones out" during the seizure and may seem confused, experience deja vu, laugh, feel afraid, see things that are not there, or smell something bad. The person may also do something over and over again, like button and rebutton a shirt.

In generalized seizures, a larger part of the brain is involved in the seizure. Often, parts of both hemispheres (halves of the brain) are affected. These seizures can be more specifically called:

Tonic-clonic - The person faints, and starts having involuntary jerking motions. They may bite their tongue, scream, drool, urinate or defecate. This kind of seizure often follows an aura, or strange feeling the person has, although not all people who have these seizures get these feelings. Tonic-clonic seizures can last up to 20 minutes.

Absence - People having absence seizures often look like they are just "spaced out." They do not fall to the ground or have jerking movements, but they do not seem to hear or notice anything around them. Other people may not notice that the person is having a seizure at all. The person may simply freeze in place and pick up where they left off when the seizure is over. The person having the seizure usually does not remember it afterward. This kind of seizure only lasts up to 10 seconds.

Myoclonic - A myoclonic jerk is a sudden jerking motion, usually on both sides of the body. This kind of seizure is most common in children under 5. Myoclonic seizures can be seen in adults, who tend of have myoclonic jerks when they are falling asleep or already asleep. Children can have these myoclonic jerks while awake.

Certain types of seizures point to a disorder called epilepsy, where the nerves do not work as they should. They carry the wrong messages to the brain so that the person moves uncontrollably or sees, hears, smells, feels, or tastes things that are not there. Medicine can be taken to prevent this from happening.

This usually only causes seizures in children from 3 months to 6 years old.[5] Seizures that are caused by fever are called febrile seizures. Children usually grow out of them.[5] However, an adult can have a seizure from a very high fever.